The term "anhydrous hydrogen fluoride" is used here to denote a hydrogen fluoride obtained by a conventional technical process. In particular, its water content should be below 5000 ppm.
Pure anhydrous hydrogen fluoride is an important chemical product for a large number of applications and the abovementioned impurities are found to be troublesome accompanying substances in anhydrous commercial hydrogen fluoride.
Distillative processes are already in use for the purification of anhydrous commercial hydrogen fluoride, for example as described in U.S. Pat. No. 3,687,622. Distillative processes carried out with the addition of auxiliary substances are also known (U.S. Pat. No. 4,756,899) but these processes are technically complicated and not always capable of yielding sufficiently pure products. Moreover, distillative processes invariably give rise to product fractions in which the impurities have accumulated and which are very limited in their use.
Both distillative processes with the addition of auxiliary agents (DD 62309) and electrolytic processes (JP 46-15768) are known for the purification of aqueous solutions of hydrogen fluoride. It is also known that in particular the element arsenic can be removed from aqueous solutions of hydrogen fluoride by passing inert gases over the hydrogen fluoride (DD 254372). The disadvantage of the electrolytic process is that some of the other elements mentioned above can only be removed very incompletely, if at all. Moreover, the product obtained by this process is, of course, an aqueous solution of hydrogen fluoride, which cannot be used universally for all subsequent processes. In addition, the preparation of anhydrous hydrogen fluoride from aqueous solutions of hydrogen fluoride can only be achieved with great difficulty. Conversely, on the other hand, aqueous solutions with varying HF contents can easily be prepared from purified anhydrous hydrogen fluoride.
The problem therefore which arose is for finding a process of purification for anhydrous commercial hydrogen fluoride in which the disadvantages of the distillative processes would be avoided and as far as possible all impurities would be removed.
This problem has been solved by the purification process according to the invention.